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Transposition Of Great Arteries

Transposition of Great Vessels

1. Definition

A. Ventriculo-arterial discordance
B. Great vessels reversed
C. Aorta anterior and slightly rightward
D. Most common CHD in infancy

2. Anatomy

A. Intact ventricular septum ("Simple" TGA) = 50%
B. VSD (perimembranous) = 25%
C. VSD and pulmonary stenosis = 25%
D. Patent foramen ovale in nearly all
E. Coarctation rare

3. Coronary patterns

A. Two coronary ostia - common
B. Single coronary - rare
C. Intramural coronary - very rare
D. All patterns have been "switched"

4. Physiology

A. Separate parallel circulation
B. Degree of cyanosis depends on mixing
C. VSD patients less cyanotic
D. LV thickness/function diminished > 1 month

5. Clinical Presentation

A. Cyanosis: simple >VSD
B. Earlier presentation: simple > VSD and PS > VSD
C. Soft systolic murmur

6. Diagnosis

A. CXR
1) Normal at birth
B. Echo
1) Posterior branching great vessel
2) Intracardiac anatomy defined
3) Coronary ostia defined
C. Catheterization
1) Septostomy or coronary anatomy

7. Medical Management

A. Correct acid-base abnormalities
B. Rashkind balloon atrial septostomy
C. PGE-1
D. Increase pulmonary blood flow / mixing

8. Disadvantages of Atrial Switch

A. SVC obstruction - Mustard > Senning
B. Supraventricular arrhythmias
C. Baffle leaks
D. Tricuspid insufficiency
E. Late RV failure

9. Steps in Arterial Switch Procedure

E. Reconstruct neo-pulmonary root - pericardium

10. Results of Arterial Switch

A. Operative mortality = 2-5%
B. Higher mortality - single coronary/intramural coronary
C. Supravalvular PS = 10-15%
D. Sinus rhythm > 95%
E. 90% survival at 5 years

11. With Coexisting VSD

A. Repair birth to 2 months
B. Standard arterial switch
C. Trans-atrial closure VSD
D. Mortality rate = 5-10%

12. VSD and PS

A. Shunt when symptomatic as infant
B. Rastelli repair - 1-2 years of age
C. Operative mortality = 5-10%
D. Late reoperation for conduit replacement

13. Summary

A. TGA/IVS simple - Arterial switch < 14 days
B. TGA/IVS simple with intramural L main - Mustard/Senning
C. TGA/VSD - neonatal switch and VSD closure
D. TGA/VSD/PS - shunt; Rastelli 1-2 years

EXTENDED OUTLINE

1. Introduction and History

A. Transposition of the great arteries was first described by Baillie in 1797
B. initially, the term transposition of the great arteries was applied to any abnormal position of the aorta relative to the pulmonary artery
C. in 1971 Van Praag clarified the definition of TGA to include only when there is ventriculararterial discordance and other abnormalities of position as malposition
D. the term transposition of the great arteries describes a cardiac anomaly with atrioventricular concordant and ventriculararterial discordant connection
E. a number of patients with TGA will have an associated VSD
F. the surgery for TGA started in 1950 with the Blalock-Hanlon operation which was an atrial septectomy which remained popular until the introduction of the Rashkind balloon atrial septostomy
G. the first successful atrial switch was accomplished by Senning in 1958
1) this was completed by using an intratrial baffle using the tissue between right atrial wall and atrial septum
H. the Mustard pericardial atrial baffle operation was introduced in 1963
I. in 1975 Jatene reported his initial successful experience with the arterial switch operation, including coronary transfer, for TGA with VSD
J. in 1983 several independent groups began to use the arterial switch operation for neonates with an intact ventricular septum as the primary procedure for TGA

Rationale for Arterial Switch Operation

2. Theoretical Consideration

A. after the arterial switch operation the left ventricle becomes the systemic ventricle which is better suited structurally and hemodynamically for the systemic circulation than the right ventricle
B. the right ventricle might also be hypoplastic to some degree in patients with TGA, and not infrequently, there is tricuspid valve anomalies

3. Mortality

A. the current mortality is 0-15% for atrial switch operations for simple TGA
B. the late mortality from the atrial switch operation is not negligible and is marked by a significant and continuous decrease in survival rate for as long as the follow-up extends
1) the ten year survival is 75-80%
2) the main causes of late mortality are arrhythmia, mechanical problems with the intraatrial baffle and right ventricular dysfunction
C. in TGA with VSD the risk of atrial switch is even higher with early mortality rates between 10-60%
1) the presence of a VSD in TGA has remained an risk factor for death after atrial switch even when the VSD is closed transatrially
D. current survival rates for arterial switch operation is 96% or higher

4. Postoperative Rhythm

A. the reported incidence of postoperative arrhythmia after atrial switch operation is 13-100%
B. various arrhythmias include sinus node dysfunction, AV block, supraventricular ectopic beats, atrial flutter, junctional rhythm and PVC’s
C. the cause of the arrhythmias may be a result of injury to the sinus node or blood supply, presence of suture material close to the node or due to the extensive incisions made
D. even though postoperatively the patient may have NSR there is still risk for losing NSR
1) in one study of 95 patients who had undergone the Mustard procedure 75% of the patients had atrial rhythm disorders by the sixth year postop
E. sudden death has been reported in patients even with NSR postop

5. Right Ventricular Dysfunction

A. most patients do not have signs of CHF after an atrial switch operation which are readily apparent clinically
B. abnormal RV function has been demonstrated by angiography and with videodensito-metric determination of ejection fraction and RV volume
C. RV dysfunction occurs more frequently with associated VSD or PDA
D. RV and LV function can be further decreased with exercise
E. RV dysfunction may be accompanied or precipitated by the presence of triscupid valve incompetence and therefore the TV may not be suited anatomically to sustain systemic pressure
F. it is felt that even only a minor number of patients have clinical symptoms of RV dysfunction after an atrial switch, abnormal systemic RV function may become a significant long-term problem over time

6. Systemic Venous Obstruction

A. the true incidence is difficult to measure
B. patients with complete obstruction of the superior limb may be asymptomatic
C. estimate of incidence can be made form post-operative hemodynamic data form 12 different institutions on 471 patients with the Mustard procedure
1) caval obstruction found in 147 patients (31%) with an incidence ranging form 0-67%
2) occurred more frequently with Dacron baffles
3) re-shaping of the baffle into a “trouser-shape” had lowered incidence to 5-10%
4) young age appears to be a risk factor
5) there is a lower reported incidence with the use of the Senning operation

7. Pulmonary Venous Obstruction

A. less common but more lethal than caval obstruction
B. usually symptomatic
C. among 433 patients post-op from Mustard procedure 41 (9%) had pulmonary venous obstruction
 may be lower with the use of the “trouser-shaped” patch or with the Senning operation

8. Special Physiologic and Anatomic Considerations in Arterial Switch Repairs

A. the feasibility of the arterial switch operation is dependent upon the status of the LV since the LV must pump against the systemic vascular resistance
B. in neonates with TGA and intact ventricular septums and no significant pulmonary stenosis, the left ventricular wall thickness is normal, but will decrease in response to the fall of pulmonary vascular resistance
C. by 2-4 months of age, the left ventricle will have adapted to the pulmonary circulation and will no longer be able to support the systemic circulation
D. it is therefore recommended that the arterial switch operation be performed in the first 2 weeks of life
E. if a VSD is present then the operation can be postponed
F. other anatomical considerations include:
1) left ventricular outflow tract obstruction
a) occurs in 10 % patients with TGA
b) due to a variety of causes including: subpulmonary membrane, abnormal mitral valve attachments to the septum, pulmonary valve abnormalities, prolapsing TV tissue
c) if the obstruction is dynamic with septal bulging it may correct with the arterial switch operation
2) mitral valve abnormalities
a) exists in up to 10% of patients with TGA
b) mitral stenosis or regurgitation may become more significant when the valve is made the systemic A-V valve
c) rarely does a mitral valve abnormality preclude the use of the arterial switch

9. Coronary Arterial Anatomy in Transposition of the Great Arteries

A. precise documentation of the coronary anatomy is critical to the performance of the arterial switch operation
B. the description of the coronary artery anatomy in TGA is also dependent upon correct anatomical description of the aorta relative to the pulmonary artery
C. enumerative system:
1) based on the observation that the coronary arteries arise from the sinuses that face the pulmonary root
2) the observer is positioned in the nonfacing sinus looking toward the pulmonary artery
3) the sinus on the right is called sinus 1 and the sinus on the right is called sinus 2
4) the three main coronaries are considered separately- RCA-R LAD-L and Cx
5) the pattern of branching are then specified by assigning each coronary to its sinus starting with sinus 1 and enumerating all three in a counterclockwise fashion
6) 70% have the 1LCx- 2R pattern, 14% have the 1L-2CxR pattern
7) when the aorta is either directly anterior, right anterior, or left anterior, the most common type is 1LCx- 2R pattern and when the aorta is side-by-side the PA the relatively rarer types of branching are almost always found

10. Coronary Ostia

A. in most cases the orifice of the coronary artery is situated approximately in the middle of the sinus of Valsalva just below the sinutubular junction
B. minor deviations from this central position is found frequently
C. in approximately 10% cases the orifice of a coronary artery will arise close to one of the valve commissures
D. ostia can also arise above the commissures in the tubular portion of the aorta
E. occasionally two ostia will arise from the same sinus (usually sinus 2)
F. sometimes a coronary artery will take an intramural course
G. usually courses between the aorta and pulmonary artery
H. most commonly involves the LAD
I. the proximal aspect of the coronary artery is completely embedded in the wall of the aorta

11. Current Management

A. diagnosis can be made with 2-D echocardiography
1) ECHO can define the VSD anatomy, mitral valve morphology and the anatomy of the left ventricular outflow tract
2) ECHO can delineate the proximal portions of the coronaries (including intramural)
3) can study the direction of the ventricular septum bowing in order to ascertain the relative LV and RV pressures
a) if the LV to RV pressure ratio is <0.6 there is an increased probability for LV failure after an arterial switch operation
4) most neonates can be operated on the basis of the ECHO findings
5) cardiac catheterization is performed when there is uncertainty about the presence of a left ventricular outflow tract obstruction or to study aortic arch anomalies
B. patients with an intact ventricular septum or with a small VSD are offered the arterial switch operation as primary treatment
C. balloon atrial septostomy can be performed in order to stabilize the neonate prior to definitive repair
D. when the LV to RV pressure ratio is <0.6, these patients can undergo pulmonary artery banding and systemic to pulmonary artery shunt placement in order to condition the left ventricle prior to the arterial switch procedure
E. in patients with a nonrestrictive VSD, the arterial switch operation can be performed beyond the neonatal period
F. fixed LV outflow obstruction or significant pulmonary valve stenosis are contraindications to the arterial switch operation

Surgical Technique

12. Technique of Operation

A. performed via median sternotomy
B. aorta and pulmonary arteries are dissected with mobilization of the branch PA’s to the hilum of the lung on either side
C. the aorta is cannulated as distal as possible and later transected
D. the pulmonary artery is is transected a few millimeters proximal to the bifurcation
E. the coronary arteries are mobilized by excising the ostia with a button of tissue
F. the coronary arteries are then re-implanted into the neo-aorta
G. the neoaorta is then constructed
1) the LeCompte maneuver is completed by threading the aorta beneath the bifurcation of the PA
H. the defects in the neo-pulmonary artery are patched with autologous pericardium and anastomosis is completed
I. when a VSD is present it is repaired via the right atrial approach or via the proximal aorta or pulmonary artery

13. Surgical Implications of Coronary Artery Anatomy

A. although different coronary arterial branching patterns are seen in TGA, 4 variations account for approximately 92% of them
B. all variations of coronary artery anatomy are amenable to the arterial switch operation
C. a double coronary ostium should be excised together and transferred
D. eccentrically located ostia can be excised without difficulty
E. in order to avoid inadvertent injury to a high orifice, the aorta should be opened anteriorly and the ostia identified prior to complete transection
F. if the coronary artery is intramural then the intramural portion should be excised en bloc form the aortic wall

Results

14. Survival

A. in a multi-institutional study of 513 patients with TGA+/- VSD the 1 month and 1 year survival was 84% and 82% respectively
B. as of the mid-1990’s the risk of post-operative death is less than 5%

15. Risk Factors

A. presence of an intramural coronary artery
B. earlier date of operation
C. older age of patients with simple TGA
D. longer periods of circulatory arrest
E. multiple VSD’s
F. augmentation of the aortic arch
G. a number of “high risk institutions”

16. Ventricular Function

A. intermediate term follow-up data suggest that left ventricular function and mechanics remain in normal limits in patients with TGA +/- VSD after arterial switch operation in the neonatal period
B. one group reported better systemic ventricular function after the arterial switch operation than those having Senning operations
C. other studies have confirmed that left ventricular size and function continue to be normal with long-term follow-up

17. Rhythm Disturbances

A. compared to atrial switch procedures, the incidence of post-operative arrhythmias is low
B. in one study from the Boston Children’s Hospital with 364 patients after arterial switch operation, 96% were in sinus rhythm on ECG and 99% on 24 hour Holter monitoring

18. Aortic and Pulmonary Anastomosis

A. RV outflow obstruction occurs in 5-10% of patients, usually within 6-9 months after repair
B. using a single pantaloon pericardial patch for the pulmonary artery had lowered this complication to less than 5%
C. usually the obstruction is localized to the pulmonary trunk presumably secondary to inadequate growth
D. treatment is balloon angioplasty or surgical patch angioplasty
E. left outflow tract obstruction is extremely uncommon after arterial switch operations

19. Neoaortic Valve Incompetence

A. experimental evidence suggest that the pulmonary root is capable of withstanding diastoltic pressure loading up to 200 mm Hg without dilatation or rupture
B. in the author’s experience, 30% of patients had mild or trivial aortic regurgitation with 5% having moderate incompetence; reoperation for insufficiency is rare

The Rastelli Procedure for Transposition of the Great Vessels, Pulmonary Stenosis, and Ventricular Septal Defect

20. Introduction

A. candidates for the Rastelli procedure include patients with transposition of the great vessels with fixed obstruction of the left ventricular (pulmonary) outflow tract with a ventricular septal defect
B. the Rastelli procedure restores ventriculoarterial concordance and relieves obstruction of the pulmonary outflow tract
C. preoperative assessment includes echocardiography, cardiac catheterization and angiography
D. the best candidates are those patients with D-transposition of the great vessels and a perimembranous subaortic ventricular septal defect
E. straddling of either AV valve increases the risk or precludes the
Rastelli procedure

21. Technique

A. involves construction of an intracardiac tunnel that results in closure of the VSD in such a way that as to direct left ventricular outflow through the VSD toward the aortic valve
B. enlargement of the VSD is sometimes necessary and requires resection of the infundibular septum
C. the connection between the left ventricle and the pulmonary artery is interrupted by division of the main PA with suture closure of the proximal end or by patch closure of the pulmonary valve
D. the right ventricle is connected to the distal PA with a valved extracardiac conduit
E. the conduit may be a pulmonary or aortic homograft

22. Results

A. Mayo Clinic experience
1) series of 117 patients
2) all patients have D-transposition, VSD, and pulmonary stenosis
3) age range 4 months to 29 years
4) 68% patients had received previous palliative surgery (most had systemic to pulmonary shunt)
5) overall mortality was 16 %
a) influenced by young age <5 years and small size of patient
b) also related to position of VSD with best results with perimembranous VSD’s
c) late deaths are due to sudden death and pulmonary hypertension, left ventricular dysfunction, mitral insufficiency and bacterial endocarditis
6) ten year survival was 61 %
7) most common cause of for reoperation is obstruction of the extracardiac conduit
a) may fail secondary to calcification or anterior compresion esp. in irradiated homografts and valved dacron conduits
b) in recent yearts cryopreserved aortic and pulmonary valved homografts have been conduit of choice
c) probability of conduit replacement is 62% at 10 years and 80% at 15 years

23. Technical Modifications

A. modified Rastelli procedure- avoids use of extracardiac conduit by anastomosing PA’s directly to the right ventriculotomy
1) distal PA confluence is transplanted anterior to ascending aorta and anastomosed to the RV
2) allows the procedure to be done in small infants
3) long term results are unknown
B. for patients with an intact VSD, transposition and PS a VSD can be created and a Rastelli procedure can be completed
1) historically these patients received a Mustard or Senning procedure
2) the VSD is created in the infundibular septum